BOP Testing and It's Availability on Demand-A Case Study

Abstract Blowout Preventer (BOP) is an integral component of defense in depth approach adopted in deepwater drilling operations. Regulatory bodies require frequent testing of these barriers, to make sure that they will be available to perform their intended functions when demand arrives. As BOP works only in demand mode, therefore the calculation of average probability of failure on demand (PFDavg) is one of the technique that can provide the critical information about the availability of these barriers. In this study PFDavg formulation is used to carry out s systematic performance evaluation a BOP's barrier elements. A sensitivity analysis is also performed to account for some of the real demand conditions that cannot be tested during routine tests, an example is the testing of shearing capability of blind shear rams. Multilevel test formulations are used that accommodates both of proof test and partial stroke testing concepts. The interdependency of these barrier elements is modeled by using beta factor model, which account for common cause failures. The results are presented for three flow paths of open wellbore flow, flow through drillpipe-casing annulus and flow through drillpipe. Corresponding BOP's barrier elements are used to estimate the availability of these barriers when they are demanded. The analysis results indicate high common cause failures of BOP's main control system with an average value of 0.25. Which is a significantly high dependency of both of the BOP's control pods on some of the common elements that can fail them simultaneously. The results also show that average availability of drillpipe-casing annular and open-hole barrier channels is dominated by the BOP's main control system, mainly due to its high failure rates. The analysis also revealed that a beta factor contribution significantly impacts the unavailability of drillpipe-casing annular channel barrier elements. Results for other demand scenarios and combination of working of these barrier elements are also presented. The presented results highlight some of the critical safety measures of BOP's barrier element performance and also highlight some of the deficiency areas that need to be taken care of to improve the system's performance. It is therefore hoped that the presented results will be helpful to gain insight into different modes of operation and in improving the system's performance.